Pump with quick discharge function

ABSTRACT

A pump includes a chamber defined by a piston movable in a body comprising an intake opening able to communicate with the chamber and a first non-return member authorizing passage of fluid from the opening toward the chamber, and prohibiting the passage from the chamber toward the opening. An expulsion opening is between the chamber and a duct, and a second non-return member authorizes passage of fluid from the chamber toward the duct, and prohibits passage from the duct toward the chamber. The body includes a discharge opening communicating with the duct and able to communicate with the opening, and a third non-return member movable between an open position, in which the duct communicates with the opening, and a closed position prohibiting the passage of fluid between the duct and the opening. The pump includes a member to move the third non-return member.

RELATED APPLICATION

This application claims priority to FR 15 51595, filed Feb. 25, 2015.

TECHNICAL FIELD

The present invention relates to a pump, designed to increase the pressure in an enclosed space, in particular to act on a pressure-sensitive element, for example a pneumatic actuator.

BACKGROUND

Already known in the state of the art is a pump including a hollow body and a piston, housed in the hollow body movably in a longitudinal direction, the piston defining, with the hollow body, a compression chamber with a variable volume based on a position of the piston in the longitudinal direction. The hollow body typically includes: an intake opening, designed to communicate with a fluid source and able to communicate with the compression chamber; a first non-return arranged between the intake opening and the compression chamber, which allows the passage of fluid from the intake opening to the compression chamber and prohibits the passage of fluid from the compression chamber to the intake chamber; an expulsion opening, which emerges in the compression chamber and communicates with an expulsion duct; and a second non-return arranged between the compression chamber and the expulsion duct, which allows the passage of fluid from compression chamber to the expulsion duct and prohibits the passage of fluid from the expulsion duct to the compression chamber.

When the piston moves in a first direction, the volume of the compression chamber increases and fluid fills the compression chamber by passing through the intake opening.

When the piston moves in a second direction opposite the first, the volume of the compression chamber decreases and the fluid is expelled through the expulsion opening. The first and second non-returns allow the fluid to flow only in one direction.

By applying oscillating movements to the piston in the first direction, then the second direction along the longitudinal direction, this piston expels a desired quantity of fluid in the expulsion duct. When this expulsion duct is connected to an enclosed space, the pressure in the enclosed space then increases. The invention also aims to improve such a pump, in particular for applications where a quick return to the initial position may be desired.

SUMMARY

To that end, the invention in particular relates to a pump including a hollow body and a piston, housed in the hollow body movably in a longitudinal direction, defining, with the hollow body, a compression chamber with a variable volume depending on the position of the piston in the longitudinal direction, the hollow body including: an intake opening designed to communicate with a fluid source and able to communicate with the compression chamber,

a first non-return member arranged between the intake opening and the compression chamber to allow the passage of fluid from the intake opening to the compression chamber, and to prohibit the passage of fluid from the compression chamber to the intake chamber,

an expulsion opening emerging in the compression chamber and communicating with an expulsion duct,

a second non-return member arranged between the compression chamber and the expulsion duct to allow the passage of fluid from compression chamber to the expulsion duct, and to prohibit the passage of fluid from the expulsion duct to the compression chamber

and wherein

the hollow body includes a discharge opening communicating with the expulsion duct and able to communicate with the intake opening, and a third non-return member movable between an open position, in which the expulsion duct communicates with the intake opening, and a closed position prohibiting the passage of fluid between the expulsion duct and the intake opening, and

the pump includes a movable element or member to move for the third non-return member.

By moving the third non-return member into the open position, the expulsion duct communicates with the intake opening, such that the high-pressure fluid contained in the expulsion duct is discharged through the intake opening, until the pressure in the expulsion duct is reduced to the pressure of the fluid source, for example the atmospheric pressure.

It is thus possible to discharge the pump quickly, making its use possible for applications where such a quick discharge is desirable.

A pump according to the invention can further comprise one or more of the following features, considered alone or in any technically possible combinations.

The displacement member includes: a ferromagnetic element movable between a first position, in which the third non-return member is in the open position, and a second position, in which the third non-return means are in the closed position, an elastic member biasing the ferromagnetic element toward its first position, and an electric coil surrounding the ferromagnetic element and electrically connected to a power supply able to apply an adjustable current. The position of the ferromagnetic element depends on the voltage of the current.

The third non-return member includes a non-return gate biased in the closed position by an elastic member, and the displacement member includes an actuating element secured to the piston and designed to cooperate with the non-return gate to move the non-return gate into the open position by pushing the non-return gate against the biasing of the elastic member, when the piston is in a predetermined discharge position, and said ferromagnetic element is formed by a rod secured to the piston.

The piston is movable, in the longitudinal direction, between: a first extreme position, in which the actuating element cooperates with the non-return gate, and in which the volume of the compression chamber is maximal, a second extreme position, in which the volume of the compression chamber is minimal, and at least one intermediate position, in which the actuating element is kept at a distance from the non-return gate.

The third non-return member includes a non-return gate, the ferromagnetic element being formed by this non-return gate.

The piston includes a rod made from a ferromagnetic material, in particular soft iron, extending in the longitudinal direction, the pump including an electric coil surrounding the rod and electrically connected to a power supply able to apply a variable electric current, the position of the piston depending on the voltage of the electric current.

The intake opening includes a filter.

The pump includes a variable volume fluid reservoir forming the fluid source.

The fluid is gas, in particular air.

The invention also relates to an assembly of a pump and a pressure-sensitive controllable element controlled by the pump, wherein the pump is as previously defined, the controllable element being connected to the expulsion duct of the pump.

For example, the controllable element includes a movable membrane of an expansion vessel equipping a Rankine system, the Rankine system comprising:

an evaporator,

a steam machine arranged downstream from the evaporator,

a condenser arranged downstream from the steam machine,

a pumping device arranged downstream from the condenser, and

the expansion vessel arranged between the condenser and the pumping device, the expansion vessel including:

an enclosure,

the movable membrane, mounted movably in the enclosure and separating the enclosure into a first part communicating with the condenser and the pumping device, and a second part communicating with the expulsion duct of the pump.

According to another example, the controllable element is a valve actuator, in particular for a motor vehicle exhaust device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood using the following description, provided solely as an example and done in reference to the appended figures, in which:

FIG. 1 is a diagrammatic sectional view of an assembly of a pump according to one example embodiment and a controllable element controlled by the pump, the pump including a piston shown in an intermediate position;

FIG. 2 is a view similar to FIG. 1 of the pump in which the piston is shown in a first extreme position;

FIG. 3 is a view similar to FIG. 2 of the pump in which the piston is shown in a second extreme position;

FIG. 4 diagrammatically shows an assembly of a pump according to a second example embodiment and an element controlled by the pump;

FIG. 5 is a view similar to FIG. 4 of the pump according to FIG. 4 in a discharge situation;

FIG. 6 diagrammatically shows a pump according to a third example embodiment of the invention; and

FIG. 7 shows an assembly of a pump according to the invention and an element controllable by the pump, equipping a Rankine system.

DETAILED DESCRIPTION

FIG. 1 shows an assembly 8 including a pump 10 and a pressure-sensitive controllable element 12 that is controlled by the pump 10.

In this example, the controllable element 12 is a pneumatic actuator designed to control an exhaust valve of an exhaust device of the motor vehicle. This controllable element 12 traditionally includes a body 14 defining a chamber 16 in which a tight membrane 18 is housed separating the chamber 16 into first 16A and second 16B compartments. The membrane 18 is movable in the chamber 16, such that the volume of the compartments 16A and 16B depends on the position of this membrane 18.

The membrane 18 is connected to a rod 20, such that the movement of the membrane 18 causes the movement of the rod 20.

The actuator 12 lastly includes an elastic member 22, in particular a spring, applying an elastic biasing force, biasing the membrane 18 toward a first position, shown in FIG. 1, in which the volume of the first compartment 16A is minimal or null, and the volume of the second compartment 16B is maximal. The membrane 18 is movable to a second position, in which the volume of the first compartment 16A is maximal and the volume of the second compartment 16B is minimal or null.

The rod 20 is connected to the exhaust valve. The exhaust valve is movable between a closed position and an open position. More particularly, the exhaust valve is in the closed position when the membrane 18 is in the first position, and in the open position when the membrane 18 is in the second position.

It will be noted that the membrane 18 can assume various intermediate positions between the first and second positions, each of these intermediate positions corresponding to an intermediate position of the valve between the closed position and the open position.

In order to move the membrane 18, the pressure is varied in the first compartment 16A. Thus, by increasing this pressure, a pressure force is opposed against the elastic biasing force of the elastic member 22, which makes it possible to move the membrane 18 when the pressure force is greater than the elastic force.

Conversely, when the pressure decreases, the pressure force becomes lower than the elastic force, such that the membrane 18 is returned toward its first position by the elastic member 22.

The pressure in the first compartment 16A is controlled by the pump 10.

The pump 10 includes a hollow body 24 and a piston 26 housed in the hollow body 24 and movably in the longitudinal direction X. The hollow body 24, for example, has a generally cylindrical shape extending in the longitudinal direction X.

The piston 26 defines, with the hollow body 24, a compression chamber 28 with a variable volume based on a position of the piston 26 in the longitudinal direction X.

The piston 26 is movable in the longitudinal direction X between a first extreme position, shown in FIG. 2, in which the volume of the compression chamber 28 is maximal, and a second extreme position, shown in FIG. 3, in which the volume of the compression chamber 28 is minimal. The piston 26 can assume any intermediate position between the first and second extreme positions, and in particular a so-called idle position, shown in FIG. 1, which will be described later in more detail.

The hollow body 24 includes an intake opening 30, designed to communicate with a fluid source, and able to communicate with the compression chamber 28.

The fluid source is, for example, the atmosphere surrounding the pump 10, in which case the fluid is air. In this case, the intake opening 30 is advantageously equipped with an air filter in order to avoid any contamination of the hollow body 24 by unwanted particles and/or liquids.

Alternatively, the fluid source is formed by a reservoir connected to the intake opening 30. Such a reservoir has a variable volume, such that the pressure remains constant in this reservoir when fluid is suctioned by the pump 10. In this case, the fluid can also be air, or alternatively oil or any other possible fluid.

In the described example, the intake opening 30 communicates with the compression chamber 28 through orifices 32 arranged in the piston 26. A first non-return member 34, arranged between the intake opening 30 and the compression chamber 28, allows the passage of fluid from the intake opening 30 toward the compression chamber 28, and prohibits the passage of fluid from the compression chamber 28 toward the intake opening 30. In the described example, the first non-return member 34 is formed by a non-return membrane able to unstick from the piston 26 when fluid passes through from the intake opening 30 toward the compression chamber 28, and to press against the piston 26 so as to close off the orifices 32 to prohibit the passage of fluid from the compression chamber 28 toward the intake opening 30.

The hollow body 24 further includes an expulsion opening 36, emerging in the compression chamber 28, and communicating with the expulsion duct 38. A second non-return member 40, in particular a non-return gate of the traditional type, is arranged between the expulsion opening 36 and the expulsion duct 38 to allow the passage of fluid from the compression chamber 28 toward the expulsion duct 38, and to prohibit the passage of fluid from the expulsion duct 38 toward the compression chamber 28.

When the piston 26 moves from its idle position, shown in FIG. 1, toward its second extreme position, shown in FIG. 3, the fluid contained in the compression chamber 28 is expelled through the expulsion opening 36, this expulsion being authorized by the second non-return member 40. During this movement, the non-return membrane of the first non-return member 34 is pressed against the passage orifices 32 of the piston 26, such that the fluid does not escape through these passage orifices 32.

When the piston 26 moves from its second extreme position shown in FIG. 3 toward its idle position shown in FIG. 1, the volume of the compression chamber 28 increases, and its pressure decreases such that fluid is suctioned in this compression chamber 28. Due to the second non-return member 40, the fluid is not suctioned from the expulsion duct 38. However, the first non-return member 34 allows the passage of fluid through the passage orifices 32, such that the fluid is suctioned from the fluid source through the intake opening 30 and the passage orifices 32.

By reiterating the movements of the piston 26 described above, fluid is gradually introduced into the expulsion duct 38.

As shown in FIG. 1, the expulsion duct 38 communicates with the first compartment 16A of the actuator 12, which is an enclosed space, such that the gradual introduction of fluid in the expulsion duct 38 increases the pressure in this expulsion duct 38 and in the first compartment 16A up to a desired pressure. This pressure increase causes the movement of the membrane 18, as previously indicated.

The piston 26 includes a rod 42 made from a ferromagnetic material, in particular soft iron, extending in the longitudinal direction X in the hollow body 24.

The pump 10 then includes an electric coil 44, surrounding the rod 42, and electrically connected to a power supply able to apply a variable current to the electric coil 44. Thus, the position of the piston 26 depends on the voltage of this electric current. More particularly, an increase in the electric current tends to drive the piston 26 toward its second extreme position.

The pump 10 further includes an elastic member 46, applying an elastic force biasing the piston 26 toward its first extreme position. Thus, the magnetic force induced by the electric current flowing in the coil 44 opposes the elastic force applied by the elastic member 46 on the piston 26. The stronger the electric current is, the greater the magnetic force is, the piston 26 moving toward its second extreme position when the magnetic force is greater than the elastic force of the elastic member. Conversely, by decreasing the electric current, the magnetic force decreases, and the piston 26 moves toward its first extreme position when this magnetic force is below the elastic force applied by the elastic member 46.

The piston 26 stays in its idle position, shown in FIG. 1, when a relatively low holding current, for example 5 volts, is applied to the coil 44, in order to generate an opposite magnetic force with a value equal to the elastic force.

The hollow body 24 of the pump 10 according to the invention includes a discharge opening 48, communicating with the expulsion duct 38 and able to communicate with the intake opening 30. For example, this discharge opening 48 communicates with the expulsion duct 38 via a bypass duct 50.

A third non-return member 52 is arranged between this discharge opening 48 and this bypass duct 50. This third non-return member 52 is movable between an open position, shown in FIG. 2, in which the expulsion duct 38 communicates with the intake opening 30, and a closed position prohibiting the passage of fluid between the expulsion duct 38 and the intake opening 30.

The pump 10 includes a movable element or member 54 to move the third non-return member 52.

In the first described example, the third non-return member 52 includes a non-return gate 52A biased in the closed position by an elastic member 52B. The movable member 54 includes an actuating element 56, in particular formed by a striker, secured to the piston 26, and for example, supported by the rod 42. This actuating element 56 is designed to cooperate with the non-return gate 52A to move it into the open position, by pushing it against the biasing of the elastic member 52B, when the piston 26 is in the first extreme position. This first extreme position therefore forms a discharge position.

It will be noted that the piston 26 enters its first extreme position when the electric current flowing in the coil 44 is null, in which case no magnetic force opposes the elastic force applied by the elastic member 46 on the piston 26. The discharge can therefore be done simply and quickly, by interrupting the electric current flowing in the coil 44.

FIG. 4 shows a pump 10 according to a second example embodiment of the invention. In this FIG. 4, the elements similar to those of the preceding figures are designated by identical references.

In this example, the pump 10 is an oil pump. In this case, the actuator 12 is a jack, including a piston 58 movable in a body 60, and separating this body 60 into a first compartment 62 communicating with the evacuation duct 38 of the pump 10, and a second compartment 64.

The jack 12 also includes an elastic member 66 biasing the piston 58 toward a first position in which the first compartment 62 has a minimal or null volume. The rod 20 is secured to the piston 58 on the one hand, and to a valve element 68 on the other hand, such that this valve element 68 is movable based on the position of the piston 58 via the rod 20.

According to this second embodiment, the intake opening 30 is connected to a reservoir 70 filled with oil, and including a flexible pouch 72 with a variable volume based on the quantity of oil in that pouch 72. The pump 10 includes an intake duct 74 that extends between the intake opening 30 and the compression chamber 28.

The first non-return member 34 then includes a non-return gate authorizing the passage of fluid from the intake duct 74 toward the compression chamber 28 and prohibiting the passage of fluid from the compression chamber 28 toward the intake duct 74.

In this embodiment, the piston 26 does not include a passage opening. However, as before, the volume of the compression chamber 28 depends on the position of the piston 26.

As before, the compression chamber 28 includes an expulsion opening 36, emerging in the compression chamber 28, and communicating with the expulsion duct 38. The second non-return member 40 is arranged at this expulsion opening 36, between the compression chamber 28 and the expulsion duct 38, in order to allow the passage of oil from the compression chamber 28 toward the expulsion duct 38, and to prohibit the passage of fluid from the expulsion duct 38 toward the compression chamber 28.

The operation of this pump is identical to that of the pump according to the first embodiment.

According to this second embodiment, the discharge opening 48 is arranged in a discharge duct 76 extending between the expulsion duct 38 and the intake duct 74. The third non-return member 52 is housed in this discharge duct 76.

The movable member 54 then includes a ferromagnetic element 78 movable between a first position, in which the third non-return member 52 is in the open position, and a second position, in which the third non-return member 52 is in a closed position. The movable member 54 also includes an elastic member 80 biasing the ferromagnetic element 78 toward its first position, as well as a coil 82 surrounding the ferromagnetic element 78, and electrically connected to a power supply able to apply an adjustable current, the position of the ferromagnetic element depending on the voltage of the current. More particularly, the third non-return member 52 includes a non-return gate, with the ferromagnetic element 78 being formed by this non-return gate.

As shown in FIG. 5, when the current is interrupted in the coil 82, no magnetic force is applied on the non-return gate 78, such that it is only subject to the elastic force of the elastic member 80, which drives it toward its first position. In this position, the expulsion duct 38 communicates with the intake duct 74, such that the high-pressure oil contained in the expulsion duct 38 is evacuated toward the reservoir 70. Thus, the pump can be discharged very simply by interrupting the current flowing in the electric coil 82.

However, during normal operation of the pump, a holding current flows continuously in the coil 82 to keep the gate 78 in its closed position. The magnetic force thus applied to the gate 78, added to the pressure force from the oil contained in the expulsion duct 38, keeps the gate in the closed position against the elastic force applied by the elastic member 80.

FIG. 6 shows a pump 10 according to a third example embodiment of the invention. In this FIG. 6, the elements similar to those of the preceding figures are designated by identical references.

According to this third embodiment, the pump 10 is an air pump.

For example, the intake opening 30 is connected to a reservoir 70, including a pouch 72 with a variable volume, forming an air source. The air flows from the intake opening 30 to the compression chamber 28 via at least one intake duct 74 and by passing through the first non-return member 34. When the volume of the compression chamber 28 decreases, the air is expelled up to an expulsion duct 38, through an expulsion opening 36 including the second non-return member 40.

As in the second embodiment, the discharge opening 48 is arranged between the expulsion duct 38 and the intake duct 74, and includes a gate 78 made from a ferromagnetic material that is surrounded by an electric coil 82.

The operation of this pump 10 according to the third embodiment is similar to the operation of the pump 10 according to the second embodiment previously described.

FIG. 7 shows a Rankine system 100 using a pump 10 according to the invention, for example according to any one of the embodiments previously described. More particularly, the pump 10 is advantageously an air pump.

The Rankine system 100 traditionally includes an evaporator 102, a steam machine 104 arranged downstream from the evaporator 102, a condenser 106 arranged downstream from the steam machine 104, and a pumping device 108 arranged downstream from the condenser 106, as well as an expansion vessel 110 arranged between the condenser and the pumping device 108.

The Rankine system 100 is designed to recover the exhaust gas heat emitted by a gasoline or diesel internal combustion engine, by evaporating the working fluid, for example ethanol water, R134, R245 or any other fluid having the requisite characteristics, in the evaporator 102 generally arranged downstream from a pollution control system.

The working fluid is next expanded in the steam machine 104, of the piston engine type, the turbine type, or any other type making it possible to convert a pressurized gas at a certain temperature into mechanical work. The steam machine 104 therefore provides mechanical work, which can, for example, next be converted into electricity.

Once expanded, the fluid is condensed in the condenser 106, which is formed by a heat exchanger with a cold source, for example the cooling water of the motor vehicle or the ambient air.

Once the fluid has returned to liquid state, it is pumped by the pumping device 108 to be reintroduced into the evaporator 102. The pressure obtained in this evaporator 102 is imposed by the steam machine 104.

Such a Rankine system operates in a closed loop, without loss of working fluid.

For the proper operation of the Rankine system, it is necessary to minimize the external leaks and prohibit air from entering. Certain fluids, such as ethanol water, are completely liquid at the pressures and temperatures encountered when the vehicle is stopped (atmospheric pressures and temperatures). Air must absolutely be banished in an enclosed system, since it is compressible. Thus, if an air bubble was suctioned by the pumping device 108, the flow rate would be unpredictable. Consequently, when the vehicle is stopped and cooled, all of the fluid is in liquid form if the internal pressure of the system is at the atmospheric pressure.

Conversely, if the volume dedicated to the working fluid is constant, the internal cold pressure would decrease until reaching a pressure of approximately 0.1 bars, corresponding to the saturating steam pressure around 20 to 40° C. In other words, part of the working fluid would remain in steam form at a very low pressure and ambient temperature.

A vehicle such as a car is stopped for the majority of its lifetime. Yet under these conditions, the pressure prevailing inside is so low relative to the atmospheric pressure that the risk of introducing a little bit of air during these long exposures is high. To eliminate any leakage risk, it is necessary for the system to be at atmospheric pressure during stops of the vehicle. If the system is at atmospheric pressure when stopped without air inside, then the entire fluid circuit is in liquid form.

When the engine is turned on, the exhaust gases heat the working fluid to convert it into steam. This steam has a lower density than the corresponding liquid. The additional volume necessary for steam formation can be procured by an additional element, which is the expansion vessel 110.

The expansion vessel 110 includes an enclosure 112 and a membrane 114, mounted movably in the enclosure 112, separating the enclosure 112 into a first part 116 communicating with the condenser 106 and the pumping device 108, and a second part 118 communicating with the expulsion duct 38 of the pump 10. Thus, the pump 10 can manage the pressure in this second part 118 of the enclosure 112. This second part 118 is, for example, equipped with a pressure sensor, making it possible to determine the pressure in this second part 118.

Advantageously, the membrane 114 is made from metal to have satisfactory sealing and to prevent the migration of gas particles through this membrane during the lifetime of the vehicle.

It should be noted that the system is generally not completely tight. It is therefore preferable to store, in the expansion vessel 110, a buffer volume of working fluid that will decrease as part of the fluid from the system is lost. Such a buffer volume is sufficient to cover the leakage of the system, which is approximately 200 cm³ for the lifetime of the vehicle, which is generally 15 years and 5000 hours of use.

In such a Rankine system, once the working fluid is expanded (at the outlet of the steam machine 104), it is condensed in the condenser 106. The condenser is supplied with a low-temperature fluid (for example, engine cooling water, or ambient air). The condensation pressure depends on the temperature of this low-temperature fluid.

For certain working fluids (water, water ethanol mixture, acetone, toluene, etc., for example), the expansion vessel 110 makes it possible to account for the increased volume of the working fluid due to its passage from the liquid state to the steam state in part of the evaporator 102, in the steam machine 104 and in part of the condenser 106.

The aim of the association of the expansion vessel 110 with the condenser 106 is to ensure the lowest possible pressure at the outlet of the steam machine 104 while ensuring that the working fluid is completely liquid at the outlet of the condenser 106, and above all at the inlet of the high-pressure pump 108, in order to ensure that the latter is always pumping liquid.

It is therefore necessary to manage the pressure of the working liquid between the condenser 106 and the pump 108. To that end, the temperature of the cold source (engine water generally known in the injection computer, or ambient air, which is also measured at the engine intake) is known, as well as the flow rate of this cold source (water flow rate depends on the engine rating, and the air flow rate depends on the speed of the vehicle and/or the speed of the fan). This temperature and this flow rate make it possible to calculate the thermal flow.

It is therefore possible to know the temperature of the working fluid either by calculation or by measuring it directly. The geometric definition of the expansion vessel 110 makes it possible to know, at any point in the operation of the cycle, the resultant pressure of the working fluid. Yet in some cases, this pressure must be corrected to be sure of the working fluid state.

To adapt the pressure to the temperature of the cold source, a pressure is applied in the part 116 that is managed using the pump 10.

Advantageously, the pressure in the first part 116 is measured by the pressure sensor, which makes it possible to apply the necessary pressure to ensure that the fluid is liquid at the outlet of the condenser 106, irrespective of the temperature of the cold source.

It will be noted that the invention is not limited to the described embodiment, but could assume various alternatives.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure. 

1. A pump including a hollow body and a piston housed in the hollow body movably in a longitudinal direction, the piston defining, with the hollow body, a compression chamber with a variable volume depending on a position of the piston in the longitudinal direction, the hollow body including: an intake opening designed to communicate with a fluid source and able to communicate with the compression chamber; a first non-return member arranged between the intake opening and the compression chamber to allow the passage of fluid from the intake opening to the compression chamber, and to prohibit the passage of fluid from the compression chamber to the intake chamber; an expulsion opening emerging in the compression chamber and communicating with an expulsion duct; a second non-return member arranged between the compression chamber and the expulsion duct to allow the passage of fluid from compression chamber to the expulsion duct, and to prohibit the passage of fluid from the expulsion duct to the compression chamber; and wherein: the hollow body includes a discharge opening communicating with the expulsion duct and able to communicate with the intake opening, and a third non-return member movable between an open position, in which the expulsion duct communicates with the intake opening, and a closed position prohibiting the passage of fluid between the expulsion duct and the intake opening, and the pump includes displacement elements for moving the third non-return member.
 2. The pump according to claim 1, wherein the displacement elements include: a ferromagnetic element movable between a first position, in which the third non-return member is in the open position, and a second position, in which the third non-return member is in the closed position, a first elastic member biasing the ferromagnetic element toward its first position, and an electric coil, surrounding the ferromagnetic element and electrically connected to a power supplier able to apply an adjustable current, wherein a position of the ferromagnetic element depends on voltage of the current.
 3. The pump according to claim 2, wherein: the third non-return member includes a non-return gate biased in the closed position by a third elastic member, and the displacement elements include an actuating element secured to the piston and designed to cooperate with the non-return gate to move the non-return gate into the open position by pushing the non-return gate against the biasing of the third elastic member, and when the piston is in a predetermined discharge position, said ferromagnetic element is formed by a rod secured to the piston.
 4. The pump according to claim 3, wherein the piston is movable, in the longitudinal direction, between: a first extreme position, in which the actuating element cooperates with the non-return gate, and in which the volume of the compression chamber is maximal, a second extreme position, in which the volume of the compression chamber is minimal, and at least one intermediate position, in which the actuating element is kept at a distance from the non-return gate.
 5. The pump according to claim 2, wherein the third non-return member includes a non-return gate, said ferromagnetic element being formed by the non-return gate.
 6. The pump according to claim 1, wherein the piston includes a rod made from a ferromagnetic material and extending in the longitudinal direction, the pump including an electric coil surrounding the rod of the piston and electrically connected to a power supplier able to apply a variable electric current, wherein a position of the piston depends on voltage of the electric current.
 7. The pump according to claim 1, wherein the intake opening includes a filter.
 8. The pump according to claim 1, including a variable volume fluid reservoir forming the fluid source.
 9. The pump according to claim 1, wherein the fluid is gas, in particular air.
 10. An assembly of a pump and a pressure-sensitive controllable element controlled by the pump, wherein the pump includes a hollow body and a piston housed in the hollow body movably in a longitudinal direction, the piston defining, with the hollow body, a compression chamber with a variable volume depending on a position of the piston in the longitudinal direction, the hollow body including: an intake opening designed to communicate with a fluid source and able to communicate with the compression chamber; a first non-return member arranged between the intake opening and the compression chamber to allow the passage of fluid from the intake opening to the compression chamber, and to prohibit the passage of fluid from the compression chamber to the intake chamber; an expulsion opening emerging in the compression chamber and communicating with an expulsion duct; a second non-return member arranged between the compression chamber and the expulsion duct to allow the passage of fluid from compression chamber to the expulsion duct, and to prohibit the passage of fluid from the expulsion duct to the compression chamber; and wherein: the hollow body includes a discharge opening communicating with the expulsion duct and able to communicate with the intake opening, and a third non-return member movable between an open position, in which the expulsion duct communicates with the intake opening, and a closed position prohibiting the passage of fluid between the expulsion duct and the intake opening, and the pump includes displacement elements for moving the third non-return member, and wherein the controllable element is connected to the expulsion duct of the pump.
 11. The assembly according to claim 10, wherein the controllable element includes a movable membrane of an expansion vessel equipping a Rankine system, said Rankine system comprising: an evaporator, a steam machine arranged downstream from the evaporator, a condenser arranged downstream from the steam machine, a pumping device arranged downstream from the condenser, and the expansion vessel being arranged between the condenser and the pumping device, the expansion vessel including: an enclosure, said movable membrane, mounted movably in the enclosure and separating the enclosure into a first part communicating with the condenser and the pumping device, and a second part communicating with the expulsion duct of the pump.
 12. The assembly according to claim 10, wherein the controllable element is a valve actuator, in particular for a motor vehicle exhaust device. 